Abrasive articles



Patented June 3, 1952 UNITED STATES ABRASIVE ARTICLES Charles E. Wooddell, Garret Van Nimwegen, and

Edward T. Hager, Niagara Falls, N. Y., assignors to The Carborundum Company, Niagara Falls, N. Y.', a corporation of Delaware No Drawing. Application August 12, 1947, Serial No. 768,281

12 Claims.

This invention relates to improved abrasive articles wherein the abrasive grains are bonded with a copolymer of a conjugated diolefin with an ester of an unsaturated carboxylic acid.

This application is a continuation-in-part of our copending application Serial No. 438,814, filed April 13, 1942, now abandoned, as a continuation-in-part of copending application Serial No. 335,818, filed May 17, 1940, now abandoned.

While rubber-bonded abrasive articles have many desirable properties and can be manufactured in comparatively short periods of time, it is difiicult to obtain natural rubber of consistent quality from time to time. Natural rubber is obtained from many species of plants such as Hevea braszlz'enszs, Castilla elastica, Manihot, the guayule species, etc. Commercial rubber obtained from such different species by various methods is a somewhat indefinite mixture of resins, rubber hydrocarbon and proteins. The general formula for the rubber hydrocarbon is (C5H8)n, where n represents the degree of polymerization. The properties of commercial rubber vary with the source of the rubber latex, with the methods used to coagulate the latex, and with the methods used to remove undesirable resins and proteins from the rubber mass.

A great deal of research has been undertaken with the object of using a synthetic polymerization product which might be vulcanizable and have the desirable properties of natural vulcanized rubber and fewer of its disadvantages in the making of bonded abrasive wheels. It has been suggested for example that a synthetic polymer known briefly as chloroprene should be used in the manufacture of abrasive articles. Chloroprene or 2-ch1orobutadiene can be readily polymerized. By interrupting the process of polymerization before completion, an alpha polymer of chloroprene is obtained which is soft, plastic and soluble in benzene. The product resembles unvulcanized rubber in its physical properties and mechanical behavior. At 130 C. the alpha polymer changes into an elastic polymer in a few minutes. Catalysts such as zinc oxide accelerate this change to the elastic chloroprene. Sulphur is not necessary to bring about this change. By suitably compounding and curing chloroprene, vulcanizates can be obtained with tensile strengths of over 3000 pounds per square inch. Elongations at the breaking point are obtained of the order of 700 to 900 per cent. Efforts have been made to obtain a vulcanizate similar to hard rubber. This does not appear to be possible by the polymerization of chloroprene. These properties of polymerized chloroprene greatly limit its usefulness as a bond for abrasive articles. With elongations of the order of magnitude of 700 to 900 per cent, abrasive grain cannot be held securely enough by a chloroprene bond to make grinding wheels for processing hard materials.

In accordance with the present invention we use as a bond for abrasive articles a synthetic polymerization product which is vulcanizable to a state or condition similar to that of a vulcanized hard rubber or ebonite. Such vulcanizable polymerization products are obtained by copolymerizing a conjugated diolefin such as butadiene, or one of its homologs or substitution products, in admixture with one or more secondary monomers that will copolymerize therewith, the secondary polymerizing component functioning as a hardening monomer whereby the final polymerized, hard vulcanized bond is obtained. The bond of the present invention is the vulcanized copolymerization product obtained after blending or compounding of the previously polymerized copolymer with the necessary vulcanizers, accelerators, fillers, activators, etc., and vulcanization therewith, the copolymer being a polymerized product comprising:

(1) One or more monomers of the class of conjugated diolefins, and

(2) An ester of an unsaturated carboxylic acid.

Monomers of conjugated diolefins are characterizedby the presence within the monomer of two unsaturated bonds in conjugated position.

The existence of the two points of unsaturation makes it possible to more readily produce a polymerized form of the substance with itself and other monomers, and at the same time leave sufiicient remaining points of unsaturation to permit vulcanization and provide a source of cross-linkage and interaction with the various other constituents of the mixture, thereby obtaining an ultimate bond of high strength, hardness and durability.

For example, butadiene monomer has the formula CH2=CHCI-I =CH2, in which there are two double bonds, one between the first and second carbon atoms of the chain and the second double bond between the third and fourth carbon atoms of the chain. These double bonds are points of unsaturation; in other words, they are points in the molecule where other butadiene molecules or other chemical molecules may attach themselves or interact with the butadiene molecules to form a more complex, but modified substance. The above monomeric butadiene is I considered for purposes of the polymerization retion agents form cross-linkages to form hard vulcanizates.

Conjugated'diolefins or monomers of the butadiene type which can be used include butadiene- 1,3 and its homologs or substitution products.

Specific diolefins are butadiene-1,3, the methyl butadienes including l-methylbutadiene-IB', 2- methylbutadiene-l,3 (isoprene),- the dimethyl butadienes including 2,3-dimethylbutadiene=1,3 (methyl isoprene) and 1A-dimethylbutadiene-l,3, 2,3-diphenylbutadiene-1,3, l-vinylbutadiene lfi, 1 cyanobutadiene 1,3, 2 cyanobutadiene-l-Ii, pentadiene-l,3 (piperylene), hexadiene-l,5- (diallyl). For some purposes we may use compounds of similar composition such as divinyl ether and vinyl acetylene in place of part or all of the diolefin. I

The esters of an unsaturated carboxylic acid which we use to copolymerize with the diolefins are characterized by the presence of at least one double bond. By reason of that unsaturation in the ester the chain's normally formed by polymerizing the diolefins, or dienes, may be cross' linked, as a result of which the copolymers have a three-dimensional structure. The copolymers may also contain double bonds if the portion of the ester of the unsaturated acid which is present in the copolymer is not enough to satisfy all the double bonds of the diolefins, in which case the copolymers are vulcanizable' with sulphur. Al

ternatively, a sufiicient amount of the unsaturated ester to completely satisfy the double bonds of the diolefins may be used in which case the re= sulting copolymer is rigidified by the action of the ester or hardening monomer. 7

It is sometimes found desirable to slightly modify the hardness characteristics of the vulcanized polymerization products obtained. This is done by the cop'olymerization therewith of a third monomer which will soften or plasticize the final product to render it to some degree more flexible or elastic. Monomeric substance satisfactory for this purpose include propane, butene and isobutene.

The unsaturated acids used in making the esters employed in our copolymers may be either mono- Or polycarboxylic acids. Examples of monocarboxylic acids are the acrylic acids ineluding acrylic acid, methacrylic acid, chloracrylic acid. Examples of polycarboxylic acid are maleic and fumaric acids. Specific esters which we have employed are the methyl, ethyl, butyl and isobutyl esters of acrylic and of methac'rylic acid and like alkyl esters of maleic and fumaric' acid. Where additional unsaturation is desired, as for example where a relatively larg amount of the ester is to be included and the copolymer is to be vulcanizable, esters of unsaturated alcohols such a allyl or methallyl alcohol may be used. For certain purposes the nitro'alkyl esters of the unsaturated acids and particularly the dibasic acids have been found to be useful. Specific examples of such esters are the di-2-nitrobutyl and the di-2-rnethyl-2-nitr'opropyl esters of maleic' and fumaric acid.

Methods of making the copolymers of our invention are well known and therefore need not be specifically described. Generally speaking, the copolymers are made by polymerizing emulsions of the reactants in the presence of catalysts. The emulsion thus obtained is usually coagulated to provide the polymer as a solid which is rolled into sheet form. A typical method of making the copolymers of our invention is described in U. S. Patent No. 2,218,362, dated October 15, 1940.

The proportion of the diene to the ester may vary through a considerable range, as for example from about 50 to 90% of the diolefin to 10 to 50% of the ester. An'increase in the pr0portion of the ester tends to result in a stiffer and harder copolymer and one which can be rigidified to the condition of a hard rubber by the us of a smaller amount of sulphur. Where relatively large proportions of the diolefin or where esters containing more than one double bond are used, the copolymers may be vulcanized to a condition resembling soft rubber if a relatively small amount of vulcanizing agent is used or they may be made to resemble ebonite by employing additional amounts of vulcanizin agent, as for example up to 50% of sulphur based on the weight of the copolymer. Generally speaking, most abrasive articles are formed with the elastomers vulcanized to the rigid or vulcanit condition.

Although there are methods of making abrasive articles by the use of the emulsions, it is more common to use the copolymers in sheet form in which case the sheet should be plasticized by milling and by the addition of softeners or plasticizers. The desired softener may be the ester type such as dibutoxyethylphthalate, dibutyl phthalate or tricresyl phosphate. It may also be one of the soft coal tars, coal tar products or coumarone-indene resins. A combination of these differentsofteners is often advisable. After the copolymer has been masticated to a plastic mass, it is mixed with sulphur or other hardening agent such as zinc oxide or magnesium oxide, a filler (or reinforcer) such as hard rubber dust, gypsum or cryolite, vulcanizing accelerators, antioxidants, plasticizers or other activating or protective ingredients which may be required. This bonding mixture is then admixed with abrasive particles in the desired proportions. The abrasive mix is made by any suitable means at a temperature suificiently low to retard further polymerization and is then transferred to molds. The molded articles can be cured at temperatures of about 340 F. in -120 minutes.

The synthetic copolymer emulsion may also be used directly by coagulation on the abrasive particles together with the sulphur or other hardening agent, fillers, vulcanizing accelerators, antioxidants, plasticizers, or other activating or pro-'- tective ingredients which may be required. The residual moisture is removed by drying and the mix then transferred to molds. The moldled articles can be cured at temperatures of about 340 F. in 90-120 minutes.

The proportion of copolymer used in the abrasive mix may be from about 6-15% by weight and the abrasive grain may be present in the proportion of about 70-90% by weight. The grinding characteristics may be varied by changing the amount of total bond, the amount and kind of copolymer used, and by using modifying agents such as fillers and heat-hardenable phenolic resins. We frequently use a heat-hardenable phenol-formaldehyde condensation product in the A stage, either as a liquid or as a powder or sometimes in both states. The liquid resins exert a slight plasticizing efiect on the copolymer and where they are used the amount of conventional plasticlz'er may be reduced accordingly. These resins also act to increase the tensile strength and heat-resistance of the bond.

The bond is prepared before any abrasive grain is incorporated in the mix. The mixing operation is carried out on a pair of ordinary rubber rolls. The copolymer is passed through the cool rolls three or four times and then allowed to run around the front roll during the breaking down period. The accelerator is then added with cutting and blending. The softener or plasticizer and any liquid phenolic resin, followed by the zinc oxide and filler, are incorporated slowly with further working of the mix. Where sulphur and/or powdered resins are used they are the last ingredient added and are introduced without cutting. After thorough mixing the batch is out each way several times before removing it from the rolls.

The rolls are made slightly warm and the bond mixture is passed through the rolls to make it more plastic before the addition'of abrasive. The abrasive is added to the mix in small amounts in the manner employed in making natural rubber bonded abrasives. When all the abrasive has been added the abrasive-bond mixture is sheeted to the desired thickness and finally died out in the required shape before vulcanization. The wheels are cured two hours at 80 pounds steam and 500 pounds per square inch pressure in a mold and later finally vulcanized 16 hours at 300 F. in an oven.

Our invention makes it possible to prepare abrasive articles having widely differing grinding characteristics by varying the properties of the copolymer. Generally speaking, an increase in the proportion of the conjugated diolefin results in a copolymer which will react with more sulphur or other hardening agent and form a correspondingly more rigid vulcanizate. Simi larly, where the ester which is copolymerized with the diolefin contains more than one doublebond the cured or hardened copolymers are more rigid than where esters which have only one double bond are used. By reason of these facts it is possible to vary the properties of the copolymer through a very considerable range. Still more variation in the properties of the copolymers can be obtained by employing three-component interpolymers.

While the copolymers, suitably modified by fillers and the like, are of themselves satisfactory bonds for many purposes, we have at times found it advantageous to admix them with natural rubber. Our invention therefore contemplates the preparation of abrasive articles in which the bond contains both natural rubber and one or more of the copolymers as well as mixtures of various copolymers. The proportion of the natural and synthetic materials may be varied widely, depending upon the properties desired in the completed abrasive article.

While in general we prefer to vulcanize the bonds of our invention to an extent sufficient to convert the bond to a condition similar to that found in hard rubber or eb-onite, for certain purposes we prefer to employ the bond in a more rubbery condition. This is accomplished by selecting a copolymer which contains a relatively large amount of a conjugated diene and by using lesser amounts of vulcanizing agents. In some instances the bonds have been found to be satisfactory without vulcanization With sulphur or other vulcanizing agent, particularly where relatively large proportions of the unsaturated esters and especially esters containing more than one double bond are employed in making the copolymer.

An advantage of the invention is that synthetic polymerization products can be obtained according to specification as materials of more definite properties than commercial natural rubber which as noted earlier contains diiferent percentages of resins and proteins, which are difficult to sepmanufacture of abrasive articles and in the choice of polymerization products and modifying ingredients from the specific example which has been described by way of example without departing from the invention which is defined within the compass of the following claims.

We claim:

1. An abrasive article comprising abrasive grains and a bond therefor comprising a hardvulcanized copolymer of about 50-90% of a compound selected from the group consisting of conjugated diolefins containing from 4 to 6 carbon atoms and the methyl, phenyl, vinyl and cyano substitution products thereof with an ester of an unsaturated carboxylic acid and an alcohol selected from the group consisting of aliphatic alcohols containing from 1 to 4 carbon atoms, the nitro substitution products thereof and unsaturated monohydric alcohols.

2. An article as claimed in claim 1 wherein the ester is an ester of an acrylic acid.

3. An article as claimed in claim 2 wherein the ester is an ester of acrylic acid.

4. An article as claimed in claim 2 wherein the ester is an ester of methacrylic acid.

5. An article as claimed in claim 4 wherein the ester is methyl methacrylate.

6. An article as claimed in claim 1 wherein the ester is an ester of furnaric acid.

'7. An article as claimed in claim 1 wherein the ester is an ester of maleic acid.

8. An article as claimed in claim 1 wherein the ester is a nitroalkyl ester of an unsaturated dicarboxylic acid.

9. An article as claimed in claim 8 wherein the ester is di-2-methyl-2-nitropropyl maleate.

10. An article as claimed in claim 8 wherein the ester is di-2-methyl-2-nitropropyl fumarate.

11. An article as claimed in claim 1 wherein the diolefin is a methyl-substituted butadiene-1,3.

12. An article as claimed in claim 11 wherein the methyl-substituted butadiene-l,3 is 2,3-dimethylbutadiene-1,3.

CHARLES E. WOODDELL. GARRET VAN NIMWEGEN. EDWARD T. HAGER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re. 1,288 Mayall Mar. 18, 1862 2,218,362 Starkweather et al. Oct. 15, 1940 2,229,880 Allison Jan. 28, 1941 2,384,683 Kistler Sept. 11, 1945 FOREIGN PATENTS Number Country Date 512,703 Great Britain Sept. 22, 1939 

1. A ABRASIVE ARTICLE COMPRISING ABRASIVE GRAINS AND A ABOND THEREFOR COMPRISING A HARDVULCANIZED COPOLYMER OF ABOUT 50-90% OF A COMPOUND SELECTED FROM THE GROUP CONSISTING OF CONJUGATED DIOLEFINS CONTAINING FROM 4 TO 6 CARBON ATOMS AND THE METHYL, PHENYL VINYL AND CYANO SUBSTITUTION PRODUCTS THEREOF WITH AN ESTER OF AN UNSATURATED CARBOXYLIC ACID AND AN ALCOHOL SELECTED FROM THE GROUP CONSISTING OF ALIPHATIC ALCOHOLS CONTAINING FROM 1 TO 4 CARBON ATOMS, THE NITRO SUBSTITUTON PRODUCTS THEREOF AND UNSATURATED MONOHYDRIC ALCOHOLS. 